Terpenes and sterols manifest a variety of biological functions and activities as hormones, plant regulatory substances, pheromones, antibiotics, and phytoalexins among others. A knowledge of the sterospecificity and mechanisms associated with individual steps in the biosynthetic pathways to them will facilitate the rational design of specific inhibitors or promoters. This research is concerned with elucidating the stereochemistry and/or mechanistic features of key biosynthetic reactions in the formation of kaurene and related polycyclic diterpenes, gibberellic acid, squalene, cholestrol, and dolichol. The biosynthesis of kaurene, beyerene, and trachylobane by soluble enzyme preparations from Marah macrocarpus and Ricinus communis is to be investigated with labelled substrates, substrate analogues, and a new intermediate. The mechanism of squalene biosynthesis will be probed by synthesis and testing of the cyclobutyl isomer of presqualene pyrophosphate. The stereochemistry of the prenylation reaction forming the cis double bonds of dolichol is to be established by use of tritium-labelling. Chiral methyl groups and oxygen-18 labelling will be used to determine the stereochemistry of the methyl hydroxylation reaction which begins the conversion of kaurene to gibberellic acid. A series of 4Alpha-hydroxymethyl, 4Alpha-formyl, and 4Alpha-carboxyl Delta7-sterols proposed as intermediates in cholesterol biosynthesis are to be synthesized and the stereochemistry of the enzymatic hydroxylmethyl-formyl oxidation is to be investigated.